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The purpose of this paper is to investigate the dynamic characteristics of a motorized spindle with externally pressurized air bearings. The externally pressurized air bearings consist of a journal bearing and a double pad thrust bearing with orifice restrictors. The equations of motion for the rotor-bearing system are established considering five degrees-of-freedom (DOF). The perturbation method and the finite difference method are introduced to calculate the static and dynamic characteristics of the air bearings; and the effects of the rotating speed and tilt angle of the rotor on the dynamic characteristics of the air bearings are analyzed. With the dynamic coefficients of the air bearings and the 5DOF rotor-dynamic model obtained, the stability, the unbalance response, and the forced response of the rotor-bearing system are investigated. Finally, the static and dynamic characteristics of the spindle are verified by an experimental study.

Monolayer or ultrathin transition metal dichalcogenides cover a wide range of atomically thin twodimensional (2D) materials, whose fascinating properties have made them promising candidates for many applications. In this work, ultrathin MoS 2 flakes were successfully exfoliated, induced by bovine serum albumin (BSA) or hemoglobin (HB), under vigorous ultra-sonication. They were used as additives for water-based lubricating systems and related investigations indicated that they could improve the friction performance and anti-wear abilities at a relatively low concentration: 0.10 wt% of additive contents can make the average friction coefficient stabilize in the range between 0.06 and 0.08, which results from the formation of a dynamic protective film on the friction surfaces. The protein-induced ultrathin MoS 2 flakes are also expected to be useful for other hydrophilic lubrication systems, which possess great scientific value and promising application prospects compared with bulk or microscale lubricating additives.